1. Field of the Invention
This invention relates generally to material separator apparatus and is concerned more particularly with a space-saving, material separator apparatus having a plurality of interconnected separator stages.
2. Discussion of the Prior Art
In the recycling of waste material, solid municipal waste initially may be shredded and then air classified to separate the light fraction from the heavy fraction. The heavy fraction may be conveyed in a stream through a conventional magnetic separator for removal of ferromagnetic materials, such as nickel, iron, and cobalt, for examples. Thus, the stream of waste materials emerging from the magnetic separator is made up predominantly of nonferromagnetic materials which includes dielectric nonferromagnetic materials, such as plastic, rubber, and glass, for examples, as well as electrically conductive nonferromagnetic materials, such as aluminum, silver, copper, zinc, and the like.
Market analysis indicates that there is a greater demand for the electrically conductive, nonferromagnetic metals than for the other components of the heavy fraction. Consequently, although constituting only about one percent by weight of typical municipal waste, the nonferromagnetic metals nevertheless represent a significant percentage of the total resale value of recycled municipal waste. Accordingly, prior art means have been developed for separating electrically conductive items of nonferromagnetic material from the dielectric items of nonferromagnetic material in the stream emerging from the magnetic separator.
For example, U.S. Pat No. 4,003,803 granted to E. Schloemann on Jan. 18, 1977 and assigned to the assignee of this invention discloses a materials separator apparatus comprising an inclined plane having a nonmagnetic surface layer down which nonferromagnetic material slides in a stream. Disposed beneath the nonmagnetic surface layer is a steady-state magnetic series of alternate north and south poles which are substantially parallel to one another and extend at an oblique angle across the stream. As a result, electrically conductive items of nonferromagnetic material in the stream pass sequentially through a spatially alternating array of oppositely directed magnetic fields which induce eddy currents in the electrically conductive items of nonferromagnetic material. The eddy-currents coact with the magnetic fields to exert on the electrically conductive items resultant forces directed upwardly of the inclined plane and perpendicular to the angulated magnetic poles of the array. Consequently, the resultant forces have respective laterally directed components which cause the items to move laterally out of the stream while sliding longitudinally down the inclined plane. Thus, the electrically conductive items deflected laterally out of the stream are separated from the dielectric items of nonferromagnetic material in the stream.
The resultant force exerted on the electrically conductive items of nonferromagnetic material also have respective longitudinal components which are directed upwardly of the inclined plane and, consequently, may be referred to as "decelerating" force components. These decelerating force components may be rendered substantially insignificant in comparison with the force of gravity acting on the electrically conductive items by disposing the inclined plane at a suitable angle, such as greater than thirty degrees, for example, with respect to the horizontal base of the separator. Accordingly, the steeper the angle of the inclined plane, in combination with a preceding magnetic separator disposed above it to feed nonferromagnetic material onto the upper end portion of the inclined plane, the higher the resulting structure.
It may be found that one pass of the nonferromagnetic material down the inclined plane does not provide a sufficiently high separation rate of "concentrate", that is, solely electrically conductive items of nonferromagnetic material, from the "tailings", that is, solely dielectric items of nonferromagnetic material. Consequently, as shown in U.S. Pat. No. 4,029,573 granted to Theodore et al and assigned to the assignee of the invention, a second inclined plane may be disposed beneath the first inclined plane for receiving the "middlings", that is, a mixture of electrically conductive items and dielectric items of nonferromagnetic material, therefrom and reprocessing it as described. As a result, still more electrically conductive items of the nonferromagnetic material are separated from the stream, after passage of the "middlings" down the second inclined plane. However, the required slope of the second inclined plane to render the "decelerating" force components insignificant in comparison with the force of gravity increases the height of the required structure still further.
Also, it may be found that the conventional magnetic separator preceding the first inclined plane is not sufficiently strong magnetically to remove dust-size particles of ferromagnetic material from the stream. As a result, these ferromagnetic particles adhere to the smooth surface of the first inclined plane due to the attractive force exerted by the underlying magnetic array. Accordingly, the adhering ferromagnetic particles interfere with nonferromagnetic material sliding down the inclined plane, and with the lateral deflection of electrically conductive items out of the stream. Consequently, to avoid periodically cleaning the smooth surface of the inclined plane, it is necessary to provide the magnetic separator with a second magnet which is sufficiently strong to remove the dust-size particles of ferromagnetic material before they reach the first inclined plane.
Therefore, it is advantageous and desirable to provide a space-saving, materials separator apparatus with a plurality of separator stages for achieving a high separation rate of electrically conductive items from a stream of nonferromagnetic materials, and which is not adversely affected by ferromagnetic particles in the stream.